Too Number of Session for a User

Hi All,

Our customer has
.1 navision server (publishing nav 3.70 sql option db)
.2 terminal services server
(wide area users connecting nav server through)
. The aplication is based on a store addon
.60 person using navision
. 30 cashier user has a current user registry value on terminal services assigned them.
.100 number of navision user license

While we are observing Database Sessions, it is opened from File>Database>Information>Sessions some time many user has a blocked state for a while. After few minutes the block states are clearing itself.

We know that this is a normal function we could see user blocking
when intensity of operations increases.

The problem is beside blocking some users gaining sessions lets say that a random user gain 10-20 sessions within a few second and another one gaining 20-30 sessions. Few sessions repeating them until the navision license number. At this point user gets a message that telling him "Your process cancelled by another user that has your user id "

I dont understand and solved that why a user's sessions multiply itself.

Could anybody help for that tricky problem.

Kind Regards